Surveillance Definitions
AGC – Automatic Gain control is an electronic circuit that keep the video signal at a constant level (peak to peak) Increasing the video signal in low light conditions accounts for low light conditions but does produce “noise” or a grainy picture. In regular light you get a better picture with AGC turned off.
APERTURE: Like the pupil of the eye. An aperture is a hole or an opening through which light can travel. The aperture of the lens is the light gathering area, and is controlled by the iris.
ASPECT RATIO: The ratio of the vertical to the horizontal image size. Two common video aspect ratios are 4:3, and 16:9. In photography 4:3 and 3:2 are the norm. Although 16:9 are becoming more common.
ATTENUATION: Is the gradual loss in intensity of any kind of flux through a medium. This refers to signal loss in a transmission system
AUTOMATIC IRIS: – Automatic Iris or “Auto Iris” is an automatic method of opening and closing a lens of a camera in response to changes in light. The auto iris adjusts the camera to the right amount of light required for the imaging device. A tiny motor and amplifier are built in to the auto iris which receives a signal from the camera to maintain a constant single volt peak to peak video level.
AWB – Auto White Balance is an electronic process used in video cameras to retain true colors.
It is performed electronically on the basis of a white object in the picture. This allows white objects to appear white in photos or video imaging even when under halogen or incandescent lighting.
BACK FOCUS: The need for back focus occurs in a situation where the Len’s auto focus is actually focused behind the main object .
BALANCED SIGNAL: Balancing an audio or video signal across a pair of wires usually a ‘twisted pair’ cable. By sending “equal” but “opposite” signals, a balanced signaling system minimizes external interference and maintains signal quality over longer cabling distances.
BLC – Balance Light Control is a method to compensate for bright spots in a picture. It is also important to consider whether there are bright spots in the picture such as car headlights which can make identifications of the vehicle registration or model impossible. This can also be a major problem where it is necessary to identify a person who is moving from bright daylight into artificial light. This could result in the subject becoming an unidentifiable silhouette.
C-MOUNT: C-mount lenses provide a male thread which mates with a female thread on the camera and are the standard screw mounting for 2/3″ and 1″ camera lenses. The letter “C” is believed to stand for the”cine” as its original use was for movie camera lenses
CCD – Charged Coupled Devices are analog technology. The CCD camera has a slightly higher resolution than CMOS. The camera also functions better in low light. Using a 12 Volt battery, a CCD camera uses a little bit more power than the CMOS cameras which are typically powered by 9 Volts. The CCD’s size is measured diagonally usually 1/3″,1/2″ or 2/3″ usually dependent on color or black and white recording (black and white offer better recording in low light). There are two types of CCDs, frame transfer and interline transfer.
COMPOSITE VIDEO: The entire video signal comprising the sync and video information. Includes brightness/luma (Y), colors/chroma (U and V). S-video provides a better picture than composite video, but an inferior picture to component video.
CMOS – Complimentary Metal Oxide Semiconductor: Pronounced “C-Moss”. A lower resolution camera compared to a ccd model, but much more common. The advantage of a CMOS camera is that is uses lower operating current. CMOS cameras are smaller than their CCD cousins and work longer with the 9 volt battery.
DIGITAL SIGNAL: An analogue or wave signal that has been converted to a digital (discontinuous or on off state) so that it can be processed by a micro processor.
FPS – Frames per second is the number of still frames (pictures) that give the illusion of motion, which appear in a single second of time. 30Fps is considered “real time”. If you require real time viewing or recording, your cameras need to record at or above 30 fps each. Make sure to get the proper DVR that can be upgraded as your camera needs develop if you require “real time” video.
FOCAL LENGTH: The distance between the secondary principal point in the lens and the plane of the imaging device. The longer the focal length, the larger the magnification of distant objects, and the narrower the angle of view.
HAD CCD – Hole Accumulation Diode is a type of CCD sensor with a layer designed to accumulate holes (in the electronic sense), thus reducing noise level.
IR- Infra red, IR LEDS are used on Day/Night cameras which allow the camera to see in the dark.
LEVEL CONTROL: “Level” or Main iris control is used to set the auto-iris’s circuit to the users desired video level.
LINE LOCKED: Line locked means the sync pulses of cameras are locked to the AC mains frequency.
LINE POWERED: Means the camera power is supplied by the same coaxial cable as the video signal.
LUX: Lux is the measurement of light. The lower the lux, the easier it is for the camera to record in low light conditions. The Lux ratings of a camera tells you how much light is required for them to capture an image. A Rating of 1 lux would be like a full moon overhead at tropical latitudes. A Rating of 0.002 lux equates to a Moonless clear night sky with airglow.
MANUAL IRIS LENS: A lens that has a manual adjustment setting to place the iris opening (F-stop) in a fixed position. Used in settings with fixed lighting.
MINIMUM OBJECT DISTANCE (M.O.D.): The closest distance that a lens is be able to bring an object into focus. M.O.D. is measured from the vertix (front) of the lens to the object. Wide angle lenses generally have a smaller M.O.D. than large focal length lenses.
MULTIPLEXER: A Multiplexer or “mux” An electronic system that can accept a number of camera inputs and record them virtually simultaneously on one recording device. Many DVRs have built in muliplexers that allow for up to 16 channel recording.
NOISE: In a video signal noise generally refers to snow or graininess in the picture.
NTSC/EIA: The video standards produced and used in USA, Japan, and some other countries.
EIA is the monochrome standard. NTSC is the color standard which adds on top of the EIA.
OSD – On Screen Display is a method of displaying set up information or instruction on to a display monitor
Resolution – Resolution measure the cameras ability to reproduce an image. The Higher the resolution, the better the picture quality.
PAN TILT: A mounting device that can be remotely controlled or rotated in a horizontal plane (pan) or a vertical plane (tilt)
PEAK TO PEAK: The measurement of a video signal from the base (most negative) of the sync pulse to the top of the white level (most positive). For a full video signal this should be one volt. For separate sync pulses, a peak to peak voltage of 4V is commonly specified.
PINHOLE LENS: A Pinhole lens is essentially a light proof box with a small hole (aperture) in one side. Usually used for covert applications where the camera or lens needs to be hidden.
RESOLUTION: Resolution determines the fineness of an image by number of pixels in each dimension that can be displayed.
S to N Ratio – Signal to Noise Ratio is simply the ratio of the signal power and noise power, (DB), or measure of noise on a video signal. It is represented in Decibels as the level of the video signal compared to the level of noise present on that signal. The higher the signal to noise ratio the better. In a video signal an acceptable picture can be produced from values of 45dB to 60dB. Signal levels below 40dB may produce noise in a picture.
SCREEN SPLITTER: A screen splitter allows you more than one camera view on a single screen. The split can be arranged horizontal, vertical or one picture in picture.
VIDEO MOTION DETECTION: A method of detecting movement within the camera’s view or Line of Sight by the electronic analysis of the change in picture contrast, as opposed to an IR detector that search for specific changes in body heat.
WHITE LEVEL: The white level refers to the brightest (highest) part of a video signal corresponding to approximately 1.0 volt.
ZOOM LENS: A zoom lens allows you to view as a wide angle, standard, or telephoto lens by changing its focal length.
ZOOM RATIO: The ratio of the starting focal length (wide position) to the ending focal length (telephoto position) of a zoom lens. A lens with a 10X zoom ratio will magnify the image at the wide angle end by 10 times.